It is well known to the art that cellular polyurethanes are provided by the reaction of organic polyisocyanates and active hydrogen-containing organic compounds such as in particular organic polyols, in the presence of a source of blowing agent and one or more catalysts. It is also known that a number of different chemical reactions occur during polymer formation and expansion. For example, in addition to the chain-extending, urethane-forming reaction between free isocyanate groups and active hydrogen, initially formed urethane linkages bearing secondary hydrogen may also function as a source of active hydrogen and react with additional isocyanate to form cross-links between polymer chains. Further, in systems wherein the blowing agent comprises water such as, for example, flexible and high resilience foam formulations, isocyanate is also consumed by reaction with water, thereby generating carbon dioxide blowing agent in situ, and inroducing further cross-links comprising urea groups. The nature of the cellular structure and the physical and mechanical properties of the foam are influenced by the extent of such reactions, and the relative rates and point in time at which they occur. Although balancing these variables so as to achieve a particular type or grade of foam can be controlled to some extent by the functionality, molecular weight and other structural features of the polyisocyanate and active hydrogen-containing reactants, the catalyst system also plays a significant role in this respect.
Among the types of compounds that have achieved long-standing widespread commercial application as catalysts in polyurethane foam manufacture are: tertiary amines consisting of carbon, hydrogen and amino nitrogen, as typically illustrated by 1,4-diazobicyclo[2.2.2]octane ("triethylenediamine"), N,N,N',N'-tetramethyl-1,3-butanediamine and N,N-dimethylcyclohexylamine; tertiary amines consisting of carbon, hydrogen, amino nitrogen and oxygen wherein oxygen is present as ether oxygen, as typically illustrated by bis[2-(N,N-dimethylamino)ethyl]ether and N-ethylmorpholine, and tertiary amines consisting of carbon, hydrogen, amino nitrogen and oxygen wherein oxygen is present as hydroxyl as typically illustrated by N,N-dimethylethanolamine. With particular reference to the manufacture of flexible polyether polyurethane foams, such teritary amines are usually employed in combination with auxiliary catalysts comprising organic derivatives of tin such as stannous octoate and dibutyltin dilaurate in order to provide a synergistic activation of the chain-extending reaction.
A relatively recent advance in the area of cellular polyurethane technology which has triggered research effort to develop improved catalyst systems, is the advent of relatively complex multi-variable industrial scale machines for formulating polyurethane foams. Improved catalyst systems having wide processing latitude (i.e., a catalyst system which, when employed in various concentration amounts of wide latitude, produces polyurethane foams having desirable physical properties including good formulation reactivity as reflected by the rise time) are necessary in industrial scale machine formulations to produce commercially desirable polyurethane foams which require specific shapes, sizes and other physical properties (e.g., flexible, high resilience, etc.). The single commercial tertiary amine catalysts described above usually afford optimum performance at only a very narrow concentration range. Any deviation from this narrow concentration range may result in poor formulation reactivity or physical abnormalities in the polyurethane foams. The lack of discovery of a proper catalyst system having wide processing latitude in controlling the water-isocyanate reaction rate to obtain optimum formulation performance in relatively complex multi-variable industrial scale machines has been a problem in the art. In the production of at least a substantial proportion of polyurethane foams being manufactured at the present time, the aforementioned N-ethylmorpholine is used as a major component of the catalyst system.
With respect to polyurethane foam manufacture generally, it is often the preferred practice of foam manufacturers to premix the amine catalyst(s), water and foam stabilizer and to feed the aqueous premixture, commonly referred to as the activator stream, to the foam formulation as a single stream. It is often observed, however, that the mere mixing of the amine catalyst and foam stabilizer in water forms a highly viscous mixture which detracts from the processing advantage of adding these components as a combined stream rather than as individual streams. This problem is encountered in particular in the manufacture of flexible polyester polyurethane foam in which silicon-free organic surfactants are used to stabilize the foam. Thus, when certain otherwise catalytically effective amine catalysts such as bis[2-(N,N-dimethylamino)ethyl]ether, are present in combination with organic foam stabilizers, the activator stream becomes extremely viscous, approaching or actually undergoing gellation, thereby hampering or preventing pumping. In this respect, N-ethylmorpholine is used with advantage in the manufacture of flexible polyester polyurethane foam in that it is suitably employed as an amine catalyst in aqueous activator streams containing silicon-free or silicon-containing organic foam stabilizers.
The usefulness of N-ethylmorpholine in the manufacture of cellular polyurethanes, however, is attended with certain disadvantages. Thus, N-ethylmorpholine suffers the very serious drawback of having a particularly strong amine odor. The large quantities of N-ethylmorpholine which are employed relative to other catalyst components of the foam formulation causes an obnoxious atmosphere at and surrounding the foam manufacturing plant site and also provides foams having a strong residual amine odor. This compound is also associated with a number of serious toxic effects; see, for example, Plastic Technology, "Catalysts Improve As Their Need Increases" pages 47-49 (July 1972).
With a view toward providing a replacement for N-ethylmorpholine in the production of cellular polyurethanes and thereby allowing for at least a substantial reduction in the relatively large amounts presently employed, several patents have disclosed tertiary amine catalyst mixtures containing no N-ethylmorpholine and the use of said mixtures in cellular polyurethane manufacture. U.S. Pat. No. 4,012,445, U.S. Pat. No. 4,011,223, U.S. Pat. No. 3,954,749 and U.S. Pat. No. 3,821,131 relate to particular mixtures of beta-amino carbonyl catalysts wherein carbonyl is present as an amido or carboxylic acid ester group and the beta-amino group is present as dialkylamino or an N-morpholino or an N,N'-piperazino heterocyclic nucleus, and to the use of such mixtures as catalytic components in cellular polyurethane formulation. U.S. Pat. No. 4,122,038 describes and claims a catalyst combination for cellular urethane formation consisting of at least one dimethylamino ether mono-ol and at least one other tertiary amine selected from the following: bis[2-(N,N-dimethylamino)ethyl]ether, 3-dimethylamino-N,N-dimethylpropionamide, 3-dimethyl-aminopropionitrile, triethylenediamine, N,N,N',N'-tetramethyl-1,3-butanediamine and N,N-dimethylethanolamine. U.S. Pat. No. 4,049,931 discloses the uses of a catalyst system comprising a tertiary-dimethylamino ether mono-ol, including mixtures thereof, in the production of cellular urethane polymers. U.S. Pat. No. 3,925,268 relates to the use of a particular catalyst mixture comprising beta-amino nitrile catalysts with other tertiary-amines such as, for example, 3-(N,N-dimethylamino)propionitrile with dimethylethanolamine or a bis[2-(N,N-dimethylamino)alkyl]ether, in the production of cellular urethane polymers. U.S. Pat. No. 4,038,210 discloses and claims a catalyst combination for cellular urethane formation consisting of 3-(N,N-dimethylamino)propionitrile and at least one of dimethylethanolamine and bis[2-(N,N-dimethylamino)ethyl]ether. U.S. Pat. No. 4,115,321 describes and claims a catalyst combination for cellular urethane formation consisting of at least one dimethylamino ether propionitrile and at least one other tertiary amine selected from the following: bis[2, (N,N-dimethylamino)ethyl]ether, 3-dimethylamino-N,N-dimethylpropionamide, N,N-dimethylcyclohexylamine and triethylenediamine. However, none of the above-mentioned patents disclose the novel tertiary amine catalyst mixtures of this invention or their use in the manufacture of cellular polyurethanes.
It is desirable, therefore, and is a primary object of this invention, to provide tertiary amine catalyst mixtures containing at least one hydroxyalkyl piperazine in the mixture as a direct replacement for N-ethylmorpholine in the production of cellular polyurethanes and thereby allow for at least a substantial reduction in the relatively large amounts presently employed.
A further object is to provide a process for manufacturing cellular polyurethanes utilizing tertiary amine catalyst mixtures containing at least one hydroxyalkyl piperazine in the mixture as a catalytic component in the polyurethane-forming reaction, thereby, imparting good formulation reactivity to the polyurethane-forming reaction.
Yet another object is to provide cellular polyurethanes, including flexible polyester polyurethane foam, flexible polyether polyurethane foam and high resilience polyether polyurethane foam, having desirable physical properties including good breathability or porosity.
Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying description and disclosure.